A kinetic model for co-oxidation of β-carotene with oleic acid

Oxidation experiments with β-carotene in a lipid solution were conducted under various conditions of temperature, oxygen composition, and lipid content. The experimental results were compared with those using n-decane reported previously. Under all conditions, the oxidation rate in oleic acid was faster than that in n-decane. A novel kinetic model for the co-oxidation of carotene with a lipid was proposed based on the reaction mechanism, which consisted of the oxidation of carotene, the oxidation of oleic acid, and the cross-reaction of carotene with oleic acid. The model quantitatively described the oxidation behavior of carotene over a wide range of temperatures, oxygen compositions, and lipid contents.     

A rigorous kinetic model for β-carotene oxidation in the presence of an antioxidant, α-tocopherol

Oxidation of β-carotene in an inert solvent, n-decane, in the presence of various concentrations of the antioxidant α-tocopherol was studied. The progress of carotene oxidation was suppressed as long as the tocopherol remained in the system. A rigorous kinetic model for carotene oxidation in the presence of an antioxidant was proposed based on a reaction mechanism in which not only the antioxidation but also the co-oxidation and radical-exchange reaction of tocopherol with carotene were incorporated. The model quantitatively described the oxidation behavior of carotene over a wide range of temperatures, oxygen compositions, and initial antioxidant concentrations.     

Provitamin a activity and stability of β-carotene in margarine

Summary Samples of synthetic β-carotene have been assayed for vitamin A activity by the rat-curative, growth method against vitamin A acetate and compared with natural carotene. The U.S.P. XIV diet was modified by the addition of vitamin B₁₂ and α-tocopherol, which have been reported to enhance carotene utilization. Doses of vitamin A and carotene were given in cottonseed oil and in margarine; but, contrary to the report of Deuelet al. (13), no significant increase was observed in the utilization of carotene fed in margarine. The samples tested include crystalline all-trans β-carotene, micropulverized all-trans β-carotene in an oil suspension, and a series of 10 commercial margarines fortified with vitamin A. and carotene in a ratio of about 2 I.U. of vitamin A to 1 I.U. of carotene. In terms of vitamin A activity in the rat bioassay, the average potency of β-carotene in three separate bioassays of crystalline carotene was found to be 1,730,000 I.U. per gram with a standard error of ±3.5%. Thus in these assays 1 I.U. of vitamin A activity was found to be equivalent to 0.58 mcg. of all-trans β-carotene, a value in essential agreement with 0.6 mcg., the presently accepted International Standard. For margarine samples containing vitamin A and β-carotene, the average vitamin A activity in 2 bioassays was found to be very close to that calculated from the colorimetric assays, using the factor for β-carotene, 0.6 mcg.=1 I.U. The fact that other workers have reported higher provitamin A activity for β-carotene in the rat bioassay indicates the dependence of the results on the particular conditions of the bioassay. The stability of vitamin A and β-carotene in commercially prepared margarines stored at 40°F. and 75°F. was studied by accepted colorimetric procedures. Average retention values of 94% or better were obtained in margarines stored two months when the vitamin activity was supplied either from β-carotene or from vitamin A.     

Crystallization of β-carotene by a GAS process in batch Effect of operating conditions

β-carotene has been successfully recrystallized from ethyl acetate and dichloromethane solutions using carbon dioxide as antisolvent in a batch bench plant for GAS process. The aim of this work is to study the influence of operating variables (concentration, temperature, stirring rate and type of solvent) and the efficiency of the GAS process on final size of the crystals. Crystals smaller than 1 μm are obtained at temperature of 298 K, pressure of 5.8 MPa, from 1 g/l solutions and with a stirring rate of 25 Hz. GAS process yields trans isomer with high efficiency separation. Solubility of β-carotene in CO₂ plus ethyl acetate at different temperatures (298, 313 and 333 K) from 4.3 to 9.8 MPa were measured, values ranged between 0.45 (P=7.2 MPa, T=333 K) and 0.010 g/l (P=8.1 MPa, T=313 K). In addition, distribution and size of the crystals from raw and recrystallized β-carotene for the CO₂–ethyl acetate system are studied.     

Precipitation and encapsulation of β-carotene in PHBV using carbon dioxide as anti-solvent

The main objective of this work was to investigate the application of supercritical carbon dioxide as anti-solvent for the encapsulation of β-carotene in poly(hydroxybutirate-co-hydroxyvalerate) (PHBV) with dichloromethane as organic solvent using the Solution Enhanced Dispersion by Supercritical fluids (SEDS) technique. For the precipitation experiments with pure compounds the parameters investigated were the concentration of β-carotene (4 and 8 mg mL⁻¹) and PHBV (30 mg mL⁻¹) in the organic solution, pressure (from 80 to 200 bar), solution flow rate fixed at 1 mL min⁻¹, anti-solvent flow rate at 40 mL min⁻¹ and constant temperature of 313 K. Pure β-carotene precipitation indicates that an increase in pressure led in most cases to particles with larger sizes, while the opposite trend was verified for pure PHBV precipitation. The morphology of precipitated PHBV particles was spherical and was not influenced by increasing pressure. The morphology of β-carotene microparticles changed from plate-like to leaf-like particles when raising operational pressure, but was not influenced by its concentration in the organic solution as verified by micrographs of scanning electronic microscopy (SEM). For the co-precipitation experiments it was evaluated the effect of β-carotene concentration (2-30 mg mL⁻¹) in the organic solution, at fixed parameters: PHBV concentration (30 mg mL⁻¹) in organic solution, temperature at 313 K, pressure at 80 bar, solution flow rate at 1 mL min⁻¹ and anti-solvent flow rate at 40 mL min⁻¹. The encapsulation data showed that increasing the concentration of β-carotene, keeping fixed the PHBV content, results in higher percentage of solute encapsulated, increasing the encapsulation efficiency.     

Experimental measurement and correlation of solubility of β-carotene in pure and ethanol-modified subcritical water

For the first time, the solubility of β-carotene in pure and ethanol-modified subcritical water (SW) using the static method was determined. The experimental runs were performed at a temperature ranging from 298.15 to 403.15 K and 0–10% (w/w) of ethanol as a modifier at a constant pressure of 5 MPa. Samples were analyzed by UV–vis spectrophotometer. The solubility of β-carotene was found to range from 1.084 × 10⁻⁸ to 227.1 × 10⁻⁸ mol fractions in the subcritical water in above mentioned conditions. The obtained β-carotene solubility data were correlated using the linear model and modified Apelblat model. The obtained results showed the modified Apelblat model was better for estimating the solubility of β-carotene in SW. The values of the root-mean-square deviation (RMSD) between experimental and correlated data were calculated and used as the index of validity and accuracy for the model. Also, thermodynamic properties of the solution such as the Gibbs free energy of solution, enthalpy, and entropy of solution were estimated.     

Kinetic Models of β-Carotene Degradation During Air Drying of Carrots

The objective of this study was to determine the kinetic parameters of models that describe the joint influence of temperature and moisture content on the thermal degradation of β-carotene in a drying process of carrots. Two models were used: a first-order decay model with an Arrhenius and a polynomial dependency on temperature and water content, respectively, and a decay model with a WLF dependency of the decimal reduction time on glass transition temperature (Tg), with the Gordon and Taylor equation describing the influence of moisture content on Tg. Carrots were dehydrated in a cabinet air dryer at 50, 60, 70, and 80°C. Carrot samples were drawn at 20-min intervals and analyzed for moisture and β-carotene content. The parameters of the two models were estimated by nonlinear regression. In addition, the models were evaluated by comparing their predictions and experimental data during drying at 80°C of carrot slices with thickness of 3, 6, and 9 mm. Both models were found suitable for modeling the β-carotene degradation, though the lower sum of squares of residuals (SSQ) of the Tg approach model and the similar WLF parameters calculated at different drying air temperatures demonstrated the higher predictive ability of the Tg model over the more common empirical dependence model.     

Modeling of extraction of β-carotene from apricot bagasse using supercritical CO2 in packed bed extractor

This work investigates the modeling of β-carotene extraction from industrial waste product of apricot bagasse at the production of fruit juice. Shrinking core model was selected as the best mathematical model, which characterize the extraction process, after take into consideration of mass transfer mechanisms such as adsorption, diffusion, solubility, and desorption. Effect of main separation parameters such as pressure, temperature, CO₂ flow rate, and particle size on the extraction yields were researched at the supercritical fluid extraction system of laboratory scale and the results were compared with the results obtained from the solution of mathematical model.     

Air filter media functionalized with β-Cyclodextrin for efficient adsorption of volatile organic compounds

Respiratory air filter media invariably comprise a nonwoven textile fabric. The limitation of the existing fibrous air filter medium is negligible protection against hazardous volatile organic compounds (VOCs). In this study, the filter media was cross-linked with β-Cyclodextrin for the surface functionalization. The VOC adsorption performance of the functional fabric was explored for styrene, benzene, and formaldehyde and also compared with a commercial nonwoven face mask. The functionalized fabric performed much better than commercial masks with adsorption capabilities of 18.80 μg mg⁻¹ (for xylene), 14.75 μg mg⁻¹ (for benzene), and 0.06 μg mg⁻¹ (for formaldehyde). Further, the cross-linking did not affect the air permeability (204 cm³ cm⁻² s⁻¹) thus showing no resistance to breathing. β-Cyclodextrin functionalized textiles can be promising respiratory air filter media having the potential to capture a variety of VOCs yet remain breathable.     

Determination of parameters in a two-dimensional model for fixed-bed adsorbers

A new method is proposed for the determination of the parameters in a two-dimensionalmodel which characterizes the properties of axial and radial mixing and mass transport in afixed-bed adsorber.Parameter estimation for the model is carried out with methane-air-5A molecularsieve in a bed under the condition of step injection of tracer from a point on the main axis of thebed by the curve fitting method in the time domain.     

Kinetic Study of Co-b-Zeolite for Selective Catalytic Reduction

The effects of grain size, space velocity, temperature and reactant concentration on the kinetics of NOx reduction with propane over Co-b-zeolite catalyst were investigated. The external mass transfer phenomenon was examined by varying the space velocity. The results show that the transfer can be negligible when the space velocity is greater than 60000 h-1 in low temperature range. However, the transfer exists at high temperatures even when the space velocity reaches a high level. Variation of the catalyst grain size from 0.05 to 0.125 mm does not change the conversion rate of NOx. The concentrations of components, NOx, C3H8 and O2, were also investigated to have a better understanding of mechanism. Based on the experimental data, the selectivity formula was proposed. The results shows that lower temperature is helpful to get higher selectivity as the activation energy of hydrocarbon oxidation, Ea,2, is greater than that of NOx reduction, Ea,1, (Ea,2>Ea,1). High NOx concentration and low C3H8 concentration are beneficial to high selectivity. However in order to maintain high activity simultaneously, the temperature and C3H8 concentration should be high enough to promote NOx reduction. 10%(j) H2O and 75′10-6(j) SO2 were introduced into the reaction system, and Co-b-zeolite shows strong resistance to water and SO2.     

In vitro release profiles of β-carotene encapsulated in PHBV by means of supercritical carbon dioxide micronization technique

The main objective of this work was to investigate the characteristics of the in vitro release of β-carotene encapsulated in poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) using the solution enhanced dispersion by supercritical fluids (SEDS) technique. The release tests were performed using encapsulated complex with solute loading from 2.24 to 27.5% and encapsulation efficiency from 7.75 to 55.54%. The release profile assays were performed in ethyl acetate, n-hexane and anhydrous ethanol, and monitored by UV-vis spectrophotometer concentration analysis. Results indicated higher initial release rates in ethyl acetate and in n-hexane, with cumulative release percentage varying from 31.50 to 69.58% and from 42.08 to 55.96%, respectively. For anhydrous ethanol the maximum concentration was reached at 180 min, 300 min and 10 days, depending on the initial amount of β-carotene, with cumulative release ranging from 45.27 to 88.22%. In general, the β-carotene release can be controlled by the organic solvent used and by the initial amount of solute encapsulated, aspects that help the selection of the conditions to achieve the desired release profiles for a specific application.     

From laboratory to scale-up by modelling in two cases of β-carotene extraction from vegetable products

The laboratory investigation of β-carotene separation from rose hip fruits (RHFs) powder and carrot noodles (CNs) was analyzed by means of mathematical modelling, in order to develop models for process scale-up. The developed models contain parameters characterizing species transport inside and outside of vegetal material particle as well as species interphase equilibrium distribution. The model parameters were estimated by experimental data capitalization. The solvent type, liquid–solid ratio and extraction temperature were selected as process factors in β-carotene extraction. Having a significant influence on the process yield, these factors determined the values of model parameters. A model based on process control by external diffusion of extracted species and particle swelling was adopted for β-carotene extraction from RHFs, whereas an internal diffusion one was chosen to describe the process in the case of β-carotene extraction from CNs. The model parameters were identified by least squares method using theoretical and experimental data characterizing the dynamics of species extraction yield. The scale-up of counter current multistage extraction was performed through analysis of the processes studied at laboratory level.     

Advance in the Polymerization Strategy for the Synthesis of β-Peptides and β-Peptoids

Peptide mimics, possessing excellent biocompatibility and protease stability, have attracted broad attention and research in the biomedical field. β-Peptides and β-peptoids, as two types of vital peptide mimics, have demonstrated great potential in the field of foldamers, antimicrobials and protein binding, etc. Currently, the main synthetic strategies for β-peptides and β-peptoids include solid-phase synthesis and polymerization. Among them, polymerization in one-pot can minimize the repeated separation and purification used in solid-phase synthesis, and has the advantages of high efficiency and low cost, and can synthesize β-peptides and β-peptoids with high molecular weight. This review summarizes the polymerization methods for β-peptides and β-peptoids. Moreover, future developments of the polymerization method for the synthesis of β-peptides and β-peptoids will be discussed.     

Inhibitory effect of 1,3-diglycerides during adsorption of β-carotene onto attapulgite and sepiolite

The adsorption isotherms of β-carotene on attapulgite and sepiolite were measured in the presence of 1,3-diglyceride in n-hexane to elucidate the relative inhibitory power of the diglycerides, hydroxyl group, carbon number, and double bond for adsorption bleaching. The adsorption mode of β-carotene was the Langmuir type. The inhibition of β-carotene adsorption may be caused by the polarity of diglycerides and the formation of diglyceride micelles. The relative inhibitory power of 1,3-diolein, 1,3-distearin, and 1,3-dipalmitin toward β-carotene adsorption was 1.49, 1.40, and 0.99, respectively. Therefore, the relative inhibitory power due to the hydroxyl group and increase in the carbon atom of the fatty acid in glyceride was 0.41–0.49.     

A Kinetic Model Describing Antioxidation and Prooxidation of β-Carotene in the Presence of α-Tocopherol and Ascorbic Acid

β-Carotene oxidation in the presence of both lipophilic α-tocopherol and hydrophilic ascorbic acid was experimentally studied in a biphasic oil–water system. Ascorbic acid in the water phase had two opposite effects of promoting and suppressing α-tocopherol consumption in the oil phase and indirectly participated in the antioxidation and prooxidation of β-carotene in the oil phase. The drastic antioxidation of β-carotene by stopping the consumption of α-tocopherol was caused by the depletion of oxygen in the system due to the oxidation of ascorbic acid. A kinetic model was constructed by incorporating the oxidation of ascorbic acid itself in the water phase, the regeneration and consumption of α-tocopherol by ascorbic acid at the oil–water interface, and the oxygen mass transfer across the gas–oil interface and the oil–water interface. The model well described the antioxidation and prooxidation behavior of β-carotene in the presence of α-tocopherol and ascorbic acid and the oxygen concentration profiles in each phase. The model was able to effectively determine the appropriate amounts of lipophilic and hydrophilic antioxidants to prevent β-carotene oxidation under various conditions.     

Stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of α-tocopherol

The initial steps in the autoxidation of CLA methyl ester are poorly understood. The aim of this study was to determine the stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of a good hydrogen atom donor. For this purpose, 9-cis, 11-trans CLA methyl ester was autoxidized in the presence of α-tocopherol under atmospheric oxygen at 40°C in the dark. The CLA methyl ester hydroperoxides were isolated, reduced to the corresponding hydroxy derivatives, and separated by HPLC. The stereochemistry of seven hydroxy-CLA methyl esters was investigated. The position of the hydroxy group was determined by GC-MS. The geometry as well as the position of the double bonds in the alkyl chain was determined by NMR. In addition, the ¹³C NMR spectra of six hydroxy-CLA methyl esters were assigned using COSY, gradient heteronuclear multiple bond correlation, gradient heteronuclear single quantum correlation, and total correlation spectroscopy experiments. The autoxidation of 9-cis, 11-trans CLA methyl ester in the presence of a good hydrogen atom donor is stereoselective in favor of one geometric isomer, namely the 13-(R,S)-hydroperoxy-9-cis, 11-trans-octadecadienoic acid methyl ester. Three types of conjugated diene hydroperoxides are formed as primary hydroperoxides: trans,trans hydroperoxides (12-OOH-8t,10t and 9-OOH-10t,12t), a cis,trans hydroperoxide with the trans double bond adjacent to the hydroperoxide-bearing carbon atom (13-OOH-9c,11t), and a new type of cis,trans lipid hydroperoxide with the cis double bond adjacent to the hydroperoxide-bearing carbon atom (8-OOH-9c,11t). In addition, three nonkinetic hydroperoxides (13-OOH-9t,11t, 8-OOH-9t,11t, and 9-OOH-10t,12c) are formed. This study supports the theory that CLA methyl ester autoxidizes at least partly through an autocatalytic free radical reaction. The complexity of the hydroperoxide mixture is due to formation of two different pentadienyl radicals. Moreover, the stereoslectivity in favor of one geometric isomer can be explained by the selectivity of the two previous steps: the preferential formation of a W-conformer of the pentadienyl radical over the Z-conformer, and regioselectivity of the oxygen addition to the pentadienyl radical.     

Solubility of β-carotene in poly-(ɛ-caprolactone) particles produced in colloidal state by Supercritical Fluid Extraction of Emulsions (SFEE)

β-Carotene is one of the most common pigments in nature. In food applications, β-carotene formulations are very attractive because they add value to the product due to their antioxidant and pro-vitamin activities. On the other hand, miscibility and solubility data of the active compound in the carrier material are relevant for the design and development of optimum formulations. This work presents a study of the solubility of β-carotene in the range of temperature between 10 °C and 50 °C in poly-(ɛ-caprolactones) with different molecular weights (between 4000 and 25,000 g mol⁻¹) produced in colloidal state by Supercritical Fluid Extraction of Emulsions. The determination of the solubility of β-carotene was carried out by two different methods: equilibration-impregnation and equilibration-de-supersaturation. Results obtained by impregnation showed that β-carotene content impregnated into the PCLs increased gradually when the temperature was increased, obtaining maximum β-carotene contents between 87 and 191 ppm depending on the molecular weight of the polycaprolactone. However, results obtained by de-supersaturation experiments showed β-carotene contents considerably higher than those achieved in impregnation experiments, obtaining a maximum β-carotene content of 8800 ppm when polycaprolactone with the highest molecular weight was used. This result can be due to the slow release of entrapped β-carotene crystals from PCL particles.